Filming Chart Of Lighting - Canon A-1 Repair Manual

In this way, each digit of the display lights up
by means of time control at the cycle of the
multiplexer and display . In the diagram (c), the
clock pulse oscillates at a higher frequency, than
the display has the repetition of on and off as
shown in TIl T2, T3. Because of an afterimage
effect, the display which flashes on and off at a
high rate gives the impression that the display is
glowing steadily. One digit of the display is lit
for 15us and 240uS is alloted for one complete
lighting cycle. Therefore the duty cycle is 15/240 =
1/16. The characteristics of the LED is that it
has higher efficiency when flashing, on and off than
when lit constantly. And flashing LEOs save power
consumption and yet the visibility is very good due
to the higher power of illumination. The flashing
power "and cycle were determined after making many
lots of monitoring experiments .
In this fashion, the wire of the display will do
with the number of digits multiplied by seven and
with only one decoder driver. This contributes to
the cost effective reliability and power-saving
while taking into consideration the characteristics
of the human eye.
15Juee
ON
4 tE-
(Power consumption)
OFF~ ~1...
_ _ _ _ _ _
~
One cycle
I
~------
240l'So<
-------;'4'"1
Fig. 12 Filming Chart of Lighting
Computed value is output from the processer in the
form of the BCD (Binary Coded Decimal) code.
Since the display system employs a seven-segment LED
(five-segment LED for "M" display or six segments
including the decimal point for aperture indication.
One segment is not wired.), the BCD code cannot be
directly turned into the seven-segment LED indication
without any aid existing in- between.
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